The present invention generally provides shielded semiconductor electronic packages and printed circuit boards. More specifically, the present invention provides an EMI shield integrally formed within a package of a semiconductor electronic component.
Semiconductor electronic components emit electromagnetic radiation, generally in the range of 50 MHz to 3 GHz, depending on the speed of the microprocessor. As can be appreciated, with the advances in high-speed microprocessor design and the rapidly increasing capabilities of high-speed networking and switching electromagnetic radiation will often be above such a range. The problem of emittance of electromagnetic radiation is not new to designers of electronic equipment. Indeed, significant efforts are taken to reduce electromagnetic interference (EMI) and radiofrequency interference (RFI) and virtually every county has a regulating agency (FCC in the U.S., for instance) that regulates the marketing and sale of electronic equipment that do not pass stringent requirements for EMI and RFI, whether radiation is emitted or intercepted (also called susceptibility) by the electronic equipment.
Semiconductor device packages or integrated circuit chip carriers find use in a variety of electronics applications. Integrated circuits or semiconductor electronic components (collectively referred to herein as “electronic package”) are typically protected from the external environment by encapsulation with a conformal coating such as an epoxy material, transfer molding, a thermoset, or thermoplastic resin about the electronic component. Such a package provides protection from dust, humidity and other environmental factors, which can destroy or irreparably damage the circuitry of the component. Unfortunately, one problem associated with conventional packaging of the semiconductor electronic component is that such thermoplastic package does not provide shielding from electromagnetic radiation, such as RFI and EMI.
When it comes to EMI shielding at the printed circuit board or “component level,” some conventional solutions are to place a conductive surface of an EMI shield in contact with the surface ground traces either (1) directly placing a metal can in contact with a ground trace, (2) directly by metallizing a shield surface and placing it in contact with the ground trace or (3) by metallizing the “outside” surface (from the perspective of the component being shielded) and then using some method of attachment that connects the surface ground trace with the metallized outside surface. Such solutions act to protect the semiconductor electronic component from external RFI and EMI signals and to prevent the escape of RFI or EMI signals generated within the semiconductor electronic package.
The purpose of the surface ground traces, based upon the historical use of soldered metal cans, is to provide a point of contact between the metal can and printed circuit board that can be subject to standardized surface mount technology (SMT) solder reflow processes that ultimately provide a solid and permanent connection between the metal can shield and the printed circuit board.
The resultant assembly of shield and component provides adequate shielding for many applications. However, as the frequency of chips increase (e.g., greater than 3 GHz) and the data transmission rates increase, the creation of errant EMI radiation becomes much easier and more harmful to adjacent circuits and components. Indeed, with the increasing density of chips, the subject of immunity (of one chip relative to another) becomes all the more important. Thus, in general, conventional solutions will increasingly find themselves inadequate for purposes of immunity and indeed, radiated emissions, may also become an increasing issue. Moreover, for microwave devices, especially those that operate at harmonic frequencies above about 10 GHz., radiated emissions will be a significant concern.
In virtually all cases, the existing solutions are expensive and add to the cost of manufacturing electronic equipment such as cell phones, personal digital assistants, laptop computers, set-top boxes, cable modems, networking equipment including switches, bridges, and cross-connects. Moreover, as the density of electronic components on the printed circuit board increases, it may become difficult to find space on the printed circuit board to mount the EMI/RFI shields.
Therefore, a need still exists for a method to provide a low profile EMI/RFI shielding to integrated circuit packages on the printed circuit board.